Field
This application is related to wireless communications.
Related Art
3rd Generation Partnership Project (3GPP) long-term evolution (LTE) Release 8 and/or 9 (LTE Rel-8/9) may support up to 100 Mbps in a downlink (DL), and 50 Mbps in an uplink (UL) for a 2×2 configuration. The LTE DL transmission scheme is based on an Orthogonal Frequency-Division Multiple Access (OFDMA) air interface.
LTE Rel-8/9 and/or release 10 (collectively “LTE Rel-8/9/10”) systems support scalable transmission bandwidths (e.g., for purposes of flexible deployment, etc.). Such scalable transmission bandwidths may include, for example, bandwidths of 1.4, 2.5, 5, 10, 15 and 20 megahertz (MHz).
In LTE Rel-8/9 and as applicable to LTE Rel-10, each radio frame has a duration of 10 milliseconds (ms), and consists of 10 sub-frames; each of which is 1 ms. Each sub-frame consists of 2 timeslots of 0.5 ms each. There can be either seven (7) or six (6) orthogonal frequency-division multiplexing (OFDM) symbols per timeslot. The seven (7) symbols per timeslot are used with a normal cyclic prefix length, and the six (6) symbols per timeslot are used with an extended cyclic prefix length. Sub-carrier spacing for the LTE Rel-8/9 system is 15 kHz. A reduced sub-carrier spacing mode using 7.5 kHz is also possible.
A resource element (RE) corresponds to one (1) sub-carrier during one (1) OFDM symbol interval. Twelve (12) consecutive sub-carriers during a 0.5 ms timeslot constitute one (1) resource block (RB). Therefore, with seven (7) symbols per timeslot, each RB consists of 1*7=84 REs. In single-carrier configuration, a DL carrier can range from six (6) RBs up to one-hundred ten (110) RBs corresponding to an overall scalable transmission bandwidth of roughly 1 MHz to 20 MHz.
A basic time-domain unit for dynamic scheduling is one sub-frame, which consists of two consecutive timeslots. This is sometimes referred to as a resource-block pair. Certain sub-carriers on some OFDM symbols are allocated to carry pilot signals in the time-frequency grid. A number of sub-carriers at edges of the transmission bandwidth are generally not transmitted so as to comply with spectral mask requirements.
In LTE Rel-8/9, and in Rel-10 in single carrier configuration where the network may assign a user equipment (UE) to only one pair of UL and DL carriers in a frequency division duplexing (FDD) mode or one carrier time shared for UL and DL in a time division duplexing (TDD) mode, for any given subframe there may be a single Hybrid Automatic Repeat reQuest (HARQ) process active for the UL and a single HARQ process active in the DL.
LTE-Advanced with Carrier Aggregation (LTE CA Rel-10) is an evolution that aims to improve single carrier LTE data rates using, among other solutions, bandwidth extensions also referred to as carrier aggregation (CA). With CA, a UE may transmit and receive simultaneously over a physical uplink shared channel (PUSCH) and a physical downlink shared channel (PDSCH) (respectively) of multiple serving cells. For example, up to four secondary serving cells (SCells) may be used in addition to a primary serving cell (PCell), thus supporting flexible bandwidth assignments up to 100 MHz. Uplink control information (UCI), which may include HARQ acknowledgment and/or non-acknowledgement (ACK/NACK) feedback and/or channel state information (CSI), may be transmitted either on a physical uplink control channel (PUCCH) resources of the PCell or on PUSCH resources available for a serving cell configured for UL transmissions.
Control information for scheduling of PDSCH and PUSCH may be sent on one or more physical downlink control channel(s) (PDCCH). In addition to LTE Rel-8/9 scheduling using one PDCCH for a pair of UL and DL carriers, cross-carrier scheduling may also be supported by a given PDCCH; allowing the network to provide PDSCH assignments and/or PUSCH grants for transmissions in one or more other serving cells.
For a FDD LTE Rel-10 UE operating with CA, there may be one HARQ entity for each serving cell. Each HARQ entity may have up to 8 HARQ processes, e.g., one per subframe for one round-trip time (RTT). Further, for the FDD LTE Rel-10 UE operating with CA, there may be more than one HARQ process active for the UL and for the DL in any given subframe, but there may be at most one UL and one DL HARQ process per configured serving cell.